Hitherto, the following are known as methods for synthesizing optically active β-amino acid derivatives: (1) a method of synthesizing a racemate of desired amino acids, followed by optical resolution using an optically active resolving agent or an enzyme; (2) a method of the catalytic asymmetric hydrogenation of β-acylamino-α,β-unsaturated esters; or (3) a synthetic method via enamines prepared from β-ketoesters and optically active amines.
Among them, Patent Literature No. 1 discloses, as a method using a β-ketoester and an optically active amine, that a β-ketoester is reacted with an optically active phenethylamine to give an enamine, followed by reaction in the presence of a palladium catalyst and hydrogen, whereby optically active β-amino acid derivatives are synthesized. However, in the method disclosed in Patent Literature No. 1, the optically active phenethylamine which is an expensive reagent is required in an amount of more than stoichiometric amount to the β-ketoester, and the optically active phenethyl group which is a protective group has to be deprotected, rendering problems of high cost and poor operating efficiency.
In addition, Non-Patent Literature No. 1 discloses that after enamine formation by the reaction between β-ketoester and optically active phenethylamine, said enamine is reduced in the presence of sodium borohydride and an acid, yielding optically active β-amino acid derivatives. However, in the method disclosed in Non-Patent Literature No. 1, it requires an optically active amine which is an expensive reagent, in an amount of more than stoichiometric amount to the ketone, similarly as is in the method of Patent Literature No. 1, resulting in drawbacks such as high cost and poor operating efficiency due to the reaction via enamines used as intermediates.
Further, Non-Patent Literature No. 2 discloses a synthesis of optically active α-amino acid derivatives by reacting an α-keto acid with benzylamine in the presence of a catalyst and hydrogen. Non-Patent Literature No. 3 discloses a synthetic method for α-amino acid derivatives by reacting an α-keto acid with ammonium formate in the presence of a catalyst. Moreover, Non-Patent Literature No. 4 discloses a method for synthesizing N-benzyl-α-phenylalanine, which is an amino acid derivative, by reacting phenylpyruvic acid as α-keto acid with benzylamine in the presence of a catalyst and hydrogen. However, nothing is mentioned with respect to synthetic methods for optically active β-amino acid derivatives in these Non-Patent Literatures Nos. 2 to 4.
[Patent Literature No. 1] WO 00/56716
[Non-Patent Literature No. 1] (Tetrahedron:Asymmetry), 1997, vol. 8, p. 1445 to 1451.
[Non-Patent Literature No. 2] J. Org. Chem. 2003, vol. 68, p. 4067 to 4070.
[Non-Patent Literature No. 3] J. Org. Chem. 2002, vol. 67, p. 8685 to 8687.
[Non-Patent Literature No. 4] Chem. Commun. 2000, p. 1867 to 1868.